1. Field of the Invention
The present invention relates generally to a data storage apparatus for magnetic recording and regeneration, such as a hard disk drive, a magnetic tape apparatus and a magneto-optic recording apparatus, as well as a magnetic recording method and a recording method, and more particularly to a data storage apparatus ensuring an improved reliability of regenerative data by extension of magnetic transition intervals upon the recording on a medium.
2. Description of the Related Arts
A data magnetic recording system of the conventional hard disk drive has a configuration as depicted in FIG. 1 for example. The data magnetic recording system is constituted of a write unit 210 and a read unit 212. The write unit 210 comprises an encoder 216, a precoder 218 and a write driver 222, and serves to perform a magnetic recording of data on a magnetic disk by means of a head/medium 224. The read unit 212 comprises a preamplifier 226, a variable gain amplifier 228, a lowpass filter (LPF) 230, a sampler (analog-to-digital converter) 232, an equalizer 234, a Viterbi detector (maximum likelihood detector) 236, a decoder 238, a gain calculator 240, a phase calculator 242, a VFO 244 and a tap gain calculator 246. Data fed into the write unit 210 is subjected to any coding, typically RLL (Run Length Limited) coding, after which they pass through the precoder 218, with the write driver 222 feeding a write current of a rectangular waveform as indicated in FIG. 2A into the recording head to form a magnetic transition on a record medium in compliance with the codes. The direction of this write current determines the direction of fluxes on the medium as indicated in FIG. 2B, and the reversal of the write current corresponds to the magnetic transition. In the event of regenerating such fluxes on the medium by the read head, the head output signal may typically result in a signal having its peaks at the magnetic transition positions as indicated by broken lines in FIG. 2C. However, ISI (Inter-Symbol Interference) arising from the neighboring magnetic transitions gives rise to a signal as indicated by the solid line. The resultant head output signal is fed, through the preamplifier 226, the variable gain amplifier 228, the lowpass filter (LPF) 230 and the sampler 232, into the equalizer 234 which equalizes the signal into a desired waveform to thereby provide a waveform of the equalizer output signal as indicated in FIG. 2D. This equalizer output signal waveform corresponds to PR4 (partial response class 4) and is equalized so as to provide noise-free sampling values (expected values) equal to +1, 0 and xe2x88x921 as indicated by circles. The sampling values pass through the Viterbi detector 236 for demodulating the recorded codes, with the resultant codes being finally decoded into original data in the decoder 238.
However, such a data magnetic recording system of the conventional hard disk drive entails problems which follow. FIGS. 3A to 3C illustrate the problems involved in the prior art. FIGS. 3A, 3B and 3C show the write current, the state of fluxes and the head output signal, respectively. First of all, with the increasing recording density there appear media noise or nonlinear phenomena, making it difficult to correctly demodulate into original data in spite of the equalization into a desired waveform as indicated in FIG. 2D by means of the equalizer 234. In the event of recording at the minimum magnetic transition intervals (code bit interval in case of RLL code d=0) in particular, there may remarkably occur phenomena such as nonlinear transition shift known as NLTS or partial erasures known as PE. For a countermeasure against the nonlinear transition shift NLTS, a correction is currently made by means of a write pre-compensation method called WPC. In general, the nonlinear transition shift NLTS is a phenomenon in which, in case of magnetic transition consecutive on the medium, the posterior magnetic transition position is forward shifted as indicated by an arrow 250 of FIG. 3B. Thus, the write pre-compensation WPC serves to cause the record current reversal position to shift backward to the solid line position as indicated by an arrow 252 so as to ensure the formation at the original magnetic transition position. Such a write pre-compensation WPC includes one capable of varying the amount of write compensation in response to the array of the magnetic transitions without being limited to the case of minimum magnetic transition intervals, although the similarity lies in that the posterior record current reversal position is shifted backward for the formation at the original magnetic transition position. The actual state of fluxes induced by such a write current may result in zigzagged magnetic transition positions as indicated in FIG. 3B, which has been considered as a major cause of the media noise. The partial erasure PE is a nonlinear amplitude reduction phenomenon which may occur in case the zigzagged magnetic transitions are enlarged and rightward fluxes are short-circuited at a part 154 so that no magnetic transition is formed. As a countermeasure against this partial flux PE it is similarly proposed to shift the write current reversal positions to extend the magnetic transition interval, thereby compensating the amplitude. It is therefore possible to effect a correction for the average value of the nonlinear transition shift NLTS or nonlinear distortions, by use of the method for shifting the magnetic transition positions.
However, those nonlinear distortions such as the nonlinear transition shift NLTS or the partial erasure PE are intrinsically stochastic phenomena, and it is envisaged that they are observed to be included in the media noise. Although this media noise increase with the increased recording density, no other measures than using the regenerative method having a larger S/N gain were found against the once-occurred medium noise dispersion. Furthermore, one of recent problems becoming more serious is a thermal relaxation phenomenon in which the recorded signals are degraded as a result of variations with time due to heat, whereupon it has been desired to record extended magnetic transition intervals. Thus, 1-7RLL code and 2-7RLL code free from any magnetic transition consecutive have also been given a consideration, although they have a poor code rate and involve characteristic problems or a problem that the clock frequency may inconveniently increase due to the wider bands.
According to the present invention there are provided a data storage apparatus, a magnetic recording method and a storage method capable of suppressing stochastic media noise of nonlinear phenomena such as nonlinear transition shift NLTS or a partial erasure PE and capable of improving the reliability of the regenerative data.
First, the present invention provides a data storage apparatus for magnetic recording and regeneration on a medium, the data storage apparatus comprising a write unit which, only in case of occurrence of a specific code sequence, records a magnetic transition interval on the medium with an extension relative to its original magnetic transition interval; and a read unit which, in a maximum likelihood detection after equalization of read signals of the medium, adds to an expected value of the maximum likelihood detection an amplitude error arising from extension record of the magnetic transition interval relative to the original magnetic transition interval. Thus, by extending the magnetic transition interval of a specific code sequence, the present invention is able to suppress the media noise, the stochastic amount of dispersion of the non-linear phenomena such as the nonlinear transition shift NLTS or the partial erasure PE as small as possible, and is able to provide an improved reliability of the regenerative data. Also, the positive extension of the magnetic transition intervals contributes to a solution to the problems such as thermal relaxation. Furthermore, against the occurrence of any shifts of the regenerative signals from the ideal amplitude (sample value) as a result of the extended magnetic transition intervals, the degradation can be suppressed by the maximum likelihood detection through the addition of the shift-induced amplitude error to the expected value of the maximum likelihood detection.
The write unit, upon the magnetic recording on the medium, uses a coding scheme in which restriction is imposed on the magnetic transition consecutive occurring at the minimum interval, and the write unit, only in case of occurrence of a specific code sequence in the coding scheme, forms the magnetic transition interval on the medium with an extension relative to the original magnetic transition interval.
The write unit, upon the magnetic recording on the medium, uses MTR (Maximum Transition Run Trellis) codes whose magnetic transition consecutive occurring at the minimum interval has been restricted to two or less, and the write unit, only in case of occurrence of two consecutive magnetic transitions, records a first magnetic transition with a certain forward shift from its original position and a second magnetic transition with a certain backward shift from its original position. The write unit, upon the magnetic recording on the medium, uses MTR codes whose magnetic transition consecutive occurring at the minimum interval has been restricted to three or less. The write unit, in case of dibit, i.e., occurrence of two consecutive magnetic transitions, records a first magnetic transition with a certain forward shift from its original position and a second magnetic transition with a certain backward shift from its original position. The write unit, in case of Tri-bit, i.e., occurrence of three consecutive magnetic transitions, records a first magnetic transition with a certain forward shift from its original position, a second magnetic transition at its original position, and a third magnetic transition with a certain backward shift from its original position. By shifting the magnetic transition position backward, the write unit allows a combination of write pre-compensation WPC for compensating a forward shift of the nonlinear magnetic transition which may occur upon the recording.
Errors arising from the extension record of the magnetic transition intervals in the present invention may affect part of regenerating system for providing a feedback control using the regenerative signals. Thus, the read unit of the data storage apparatus in accordance with the present invention is provided with an equalizer for equalizing read signals of the medium into a desired signal waveform on the basis of an equalization error signal obtained from a difference between a pre-equalization signal and a post-equalization signal, and wherein if the read unit detects a specific code sequence recorded with certain shifts from its original magnetic transition positions, then the read unit does not use the equalization error signal at that time or does use the equalization error signal suppressed through a predetermined weighting. The read unit is provided with a PLL circuit for providing a phase control of sampling clock on the basis of a phase error signal obtained from a comparison between a reference clock and a clock extracted from an equalized regenerative signal, and wherein if the read unit detects a specific code sequence recorded with certain shifts from its original magnetic transition positions, then the read unit does not use the equalization error signal at that time or does use the equalization error signal suppressed through a predetermined weighting. The read unit is provided with an AGC circuit (gain calculator) for allowing a regenerative signal to have a desired amplitude on the basis of an amplitude error signal obtained from a comparison between an equalized regenerative signal and the desired amplitude, and wherein if the read unit detects a specific code sequence recorded with certain shifts from its original magnetic transition positions, then the read unit does not use the amplitude error signal at that time or does use the amplitude error signal suppressed through a predetermined weighting.
The data storage apparatus of the present invention further comprises a parameter regulation unit which monitors an error rate of a maximum likelihood detector through recording and regeneration of test patterns and which regulates and sets, so as to minimize the error rate, the amounts of magnetic transition extension xcex94T of a specific code sequence for use in the write unit as well as the amounts of amplitude errors xcex94V added to expected values in the maximum likelihood detection. The parameter regulation unit monitors an error rate acquired from a SAM (Sequenced Amplitude Margin) circuit by use of metric of the maximum likelihood detector, and regulates and sets each of the amounts of magnetic transition extension xcex94T of a specific code sequence for use in the write unit as well as the amounts of amplitude errors xcex94V added to the expected values in the maximum likelihood detection so as to minimize the error rate of the SAM. The SAM circuit ordinarily counts up the error if Mn is smaller than 0, that is,
Mn less than 0
where Mn=(M1xe2x88x92M2), that is, Mn is a difference between the minimum metric M1 and the second minimum metric M2, among a plurality of metrics which are cumulative values of square errors acquired in the maximum likelihood detection. However, by adding any stress thereto, the SAM circuit may count up the error if
Mn less than K
where K is a value larger than 0, thereby compulsorily allowing a frequent occurrence of errors arising from noises, to make it possible to reduce the time taken to obtain the error rate to consequently achieve a high-speed processing of the parameter regulation.
The parameter regulation unit, previous to the regulation and setting of the amounts of magnetic transition extension xcex94T upon the recording and the amounts of amplitude errors xcex94V in the maximum likelihood detection, makes regulations of the amount of write pre-compensationWPC in the write unit, the cut-off frequency Fc and the amount of boost Fb of the filter provided in the read unit, and the tap gain Gtap of the equalizer. The parameter regulation unit, after the regulation by use of a two-bit consecutive magnetic transition pattern, makes regulations of the amounts of magnetic transition extension xcex94T and the amounts of amplitude errors xcex94V by use of a three-bit or more consecutive magnetic transition pattern.
The present invention further provides a magnetic recording method for magnetic recording and regeneration on a medium, comprising:
a recording step for, only in case of occurrence of a specific code sequence, recording a magnetic transition interval on the medium with an extension relative to its original magnetic transition interval; and
a regenerating step for, in a maximum likelihood detection after equalization of read signals of the medium, adding an amplitude error arising from extension record of the magnetic transition interval relative to the original magnetic transition interval to an expected value of the maximum likelihood detection.
The details of this magnetic recording method are the same as those of the magnetic recording apparatus.
The present invention further provides a record method for magnetic recording on a medium, comprising the steps of, upon the magnetic recording on the medium, using a coding scheme in which magnetic transition consecutive occurring at the minimum interval has been restricted; and, only in case of occurrence of a specific code sequence in the coding scheme, recording a magnetic transition interval on the medium in such a manner that it becomes larger than its original magnetic transition interval.
The details of this recording method are the same as those of the write unit of the magnetic recording apparatus.
The above and other objects, aspects, features and advantages of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.